This invention relates generally to improvements in adjusting torque wrenches. More particularly, but not by way of limitation, this invention relates to an improved locking mechanism that selectively prevents and permits adjustment of the torque that is to be exerted through the wrench.
Wrenches of this general type are clearly illustrated in U.S. Pat. No. 2,792,733 issued May 21, 1957 to G. M. Walraven et al and U.S. Pat. No. 3,581,606 issued June 1, 1971 to Bosko Grabovac. Each of the foregoing patents describes a torque wrench that has a rotatable member for pre-setting the desired torque to be exerted through the wrench. Each also has some means of varying the torque and each includes a "snap-over" mechanism which, upon the torque reaching the pre-selected value, overcomes a spring load to permit the head of the wrench to pivot relative to the lever arm. Such pivotal movement is sensed by the operator and he knows that the desired torque has been exerted on the threaded fastener or the like.
While each of the foregoing devices operates generally satisfactorily, and each includes some means of locking the wrench at the pre-selected torque and unlocking the wrench so that the torque can be varied. Each has certain draw-backs that are overcome by the wrench described in this invention.
In the Walraven et al patent, the tool described therein includes a locking mechanism that is locked and unlocked by the rotation of a lock ring that is part of the grip member. The grip member is grasped by the operator to exert the torque on the wrench. Care must be exercised so that the lock ring is not inadvertently rotated during the exertion of the torque on the wrench or a variation in the pre-selected torque could occur. Also, in the Grabovac patent, the wrench described therein includes a locking mechanism that is an extension of the grip member. Unlocking is accomplished by moving, outwardly of the wrench, a knurled or serrated knob. Again, care must be exerted to be certain that the knob is not inadvertently displaced and rotated during the exertion of torque on the wrench.
This invention provides an improved adjusting torque wrench that includes a locking mechanism that is simple in construction, requires little maintenance and provides positive retention of the pre-selected torque and is not likely to be inadvertently unlocked.